There is a great deal of legacy fiber with high polarization mode dispersion (PMD) in the field. In fact, PMD is becoming a limiting factor for transmission systems with speeds of 10 Gbps or above, especially in systems using old fibers with high birefringence. There has been significant customer demand for 10 Gbps private lines. Without PMD compensation, many of these fibers may not support 10 Gbps wavelength channels. Also, the current trend in bit rates of optical communication systems is quickly moving towards 10 Gbps and 40 Gbps per wavelength channel, because it is easier to manage one single channel of high bit rate than many smaller channels of equivalent aggregate bit rate. To preserve legacy systems and thus reduce infrastructure replacement expenses, thereby meeting consumer demand at the lowest possible cost, it is important for the industry to be able to provide customers with what they want (a.k.a. 10 Gbps or above) on already installed (legacy) embedded fibers.
Research in the area of PMD mitigation has centered around adaptive cancelation and tunable PMD compensation techniques such as delaying one polarization mode with respect to the other. Compensation can be accomplished in either the electrical or optical domains. Both electronic and optical equalizers have been demonstrated in the laboratory. (See, for example, H. Bulow, et al., “Adaptive PMD mitigation at 10 Gbps using an electronic SiGe equalizer IC”, ECOC'99 paper II-138; and R. Noe, D. Sandel, M. Yoshida-Dierolf, S. Hinz, et al., Journal of Lightwave Technology, Vol. 17, p. 1602, September 1999.) PMD mitigation via single sideband modulation and principal-state launch has been proposed in METHOD AND SYSTEM FOR SINGLE-SIDEBAND OPTICAL SIGNAL GENERATION AND TRANSMISSION, U.S. application Ser. No. 09/477,816 filed Jan. 5, 2000 and commonly held and incorporated herein by reference. The present invention pertains to a diversity receiver for use in fiber optic systems.